Limited information is available about the ultimate fate of the arsenic found in chromated copper arsenate (CCA) during the service life and disposal of the treated wood product. This lack of information coupled with the large quantity of arsenic currently in service associated with treated wood (130,000 tons estimated), results in a potential risk of human and ecological exposure. The toxicity of arsenic is strongly a function of the speciation of the metalloid, with the inorganic species being more toxic than the methylated forms. Within the inorganic forms, species that are characterized by a lower valence are the most toxic. The objectives of the current study are to evaluate the toxicity of arsenic in leachates from CCA-treated wood by measuring the species of arsenic that are leached from different environmental samples. A considerable effort will be placed on method development, which will expand the applicability of cartridges designed to preserve samples in the field. Leaching will be evaluated in both laboratory and field settings. Laboratory studies will focus on standardized leaching tests aimed at simulating the impacts of rainfall, seawater, and landfill conditions. Laboratory samples evaluated will include CCA-treated wood at various retention levels. Field work will focus on evaluating the impacts of decks and marine docks constructed of CCA-treated wood on the surrounding environment. Samples will be routinely analyzed for arsenite (As(III)), arsenate (As(V)), monomethylarsonic acid (MMAA), and dimethylarsinic acid (DMAA). Other arsenic species, if any, will be detected and quantified on a periodic basis. Metals species will be routinely measured in the dissolved phase, and methods will be developed for measuring arsenic speciation within the particulate phase. Results will be used to estimate the total U.S. arsenic releases from CCA-treated wood structures. These data will be useful as inputs into environmental risk models that evaluate the probability of human disease or other environmental outcomes associated with the use or disposal of CCA-treated wood.